Method of crimping polyolefin fibers



Jan. 10, 1967 G. LOPATIN METHOD OF CRIMPING POLYOLEFIN FIBERS 4 Sheets-Sheet 1 Filed July 16, 1964 FIG.

- INVENTOR'.

GEORGE LOPATIN Wadi? 5 5m HIS ATTORNEY Jan. 10, 1967 LQPATIN 3,296,681

METHOD OF CRIMPING POLYOLEFIN FIBERS Filed July 16, 1964 4 Sheets-Sheet 2 SINGLE FILANENTS FROM POLYPROPYLENE YARNS WHICH WERE CRINPEO IN AIR no. M

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FIG. 2E M FIG. 2R A FIG. 21

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FIG. 2L M man W SINGLE FILAMENT FROM POLYPROPYLENE YARN WHICH wAs CRIMPED IN OlL nc. 2N W E smcuz FILAMENT TAKEN FRoN POLYPROPYLENE YARN AND CRIMPEO IN OIL HG. 2a W SINGLE FILANENT FROM POLYPROPYLENE YNRN WHICH \NNs cRmPEo IN N STUFFER BOX 2R SINGLE FILANENT FROM wooL YNRN SINGLE FILANENT TAKEN FROM INVENTOR: POLYPROPYLENE YARN, UNORINPED GEORGE N BY: X Baa/L HIS ATTORNEY Jan. 10, 1967 G. LOPATIN METHOD OF CRIMPING POLYOLEFIN FIBERS Filed July 16, 1964 4 Sheets-Sheet 3 FROM YARN FEED GODET ROLLS INVENTOR GEORGF HIS ATTORNEY Jan. 10, 1967 e. LOPATIN 3,296,681

METHOD OF CRIMPING POLYOLEFIN FIBERS Filed July 16, 1964 4 Sheets-Sheet 4 FIG. 4

INVENTORZ GEORGE LOPATIN BY: 5 fl k HIS ATTORNEY United States Patent M 3 296 681 METHOD OF CRIMPINC POLYQLEFHN FIBERS George Lopatin, Grinda, Califi, assignor to Shell 011 Company, New York, N.Y., a corporation of Delaware Filed July 16, 1964, Ser. No. 383,186 4 Claims. (CI. 28-72) This invention is directed to a novel method of producing bulked or texturized fibers or yarns for polypropylene, and to apparatus suitable for practicing the method.

It is known that stereoregular crystallizable polypropylene, e.g., isotactic polypropylene, has many chemical and physical properties which make it highly desirable for conversion into fibers. It may be made into monofilaments of relatively large diameter, such as are useful for conversion to bristles, ropes and the like, and into monofilaments or multifilaments of relatively small diameter, such as are useful for conversion into yarns, for production of textile fabrics, carpets, etc., or for conversion into staple for uses such as pillow fill and spun yarns.

THE STATE OF THE ART The conversion of polypropylene into filaments as practiced heretofore, and the properties of such filaments, are described in British Patent 813,891, published May 27, 1959; in an article by Coen and Conti in Materie Plastiche, volume 26, pages 723-30 (1960); and in other recent publications.

One of the characteristics of polypropylene fibers, as of other synthetic fibers produced by melt spinning, is that they are produced in the form of straight, untextured filaments. Many applications of fibers, e.g., in production of rugs, blankets, and many textiles, depend on the bulking properties of fibers, i.e., on their abilty to oppose tight packing. Such inter-fiber repulsion usually comes about from the twisted and bent configuration of the individual fibers. A separate procedure for suitably bulking, tex turizing or crimping of the fibers is therefore incorporated into the conventional fiber forming processes.

Various procedures are known for carrying out the texturizing or crimping of synthetic filaments, including polypropylene. Procedures heretofore employed for textun'zing polypropylene filaments, e.g., sufiiciently for carpet purposes, utilize mechanical deformation. They require large capital outlays and are relatively slow. The cost of texturizing is therefore substantial, especially if crimping of continuous yarns is necessary, as it is in some modern carpet-making processes.

The simplest of the known mechanical texturizing processes is stuffer box crimping, which puts sharp bends into fibers by application of mechanical pressure and heat. Fibers crimped by mechanical methods such as with the stufier box have several substantial disadvantages. Because of the regularity of the crimp the yarns tend to pack relatively easily under pressure and hence lose their bulk when, for example, they are used in carpets. The degree of crimping is difficult to control, and excessive crimping may result in mechanically weakened fibers.

In US. Patent 3,019,507 a method is proposed for introducing a crimp into continuous polypropylene yarns by stretching the yarn at the maximum safe rate at a temperature of 80 C. or below to introduce irregularly distributed internal strains, and thereafter heating the yarn at a higher temperature whereby the strains are released and a crimp is introduced. More specifically, the method of the patent comprises stretching yarns of melt extruded filaments at a stretch ratio between 122.5 and 1:55 while the yarn is at a temperature between 20 and C., stretching being carried out at the maximum safe rate for the temperature, whereby irregularly distributed internal strains are mechanically produced, and then introducing the yarns into a medium in which they are heated to temperatures above 50 C., whereby said strains are released, resulting in formation of crimps in the yarn. The illustrative examples of the patent show the second heating step being carried out at C. and C. The crimped yarns resulting from said process are said to have substantially the same crystallite orientation and the same tensile strength as the stretched and oriented yarns prior to crimpmg.

While the method of said patent is probably an improvement over the mechanical crimping methods of the prior art, it requires modification of existing yarn producing methods. It requires an unusually high stretching rate, approaching the limit at which filament breakage occurs. Furthermore, it specifically requires that stretching must be carried out at temperatures no higher than 80 C. These temperatures are lower than generally employed or considered desirable for production of polypropylene filaments.

THE METHOD OF THIS INVENTION It has now been found that polypropylene fibers can be simply treated to introduce a permanent irregular crimp of a particularly advantageous configuration, and that this can be done by operating on any previously stretched polypropylene fiber, regardless of the conditions at which it was stretched. The crimping step consists of quickly heating a previously stretched fiber or yarn in substantial ly tension-free condition to a temperature in a narrow range, namely, within about 15 C., preferably with about 10 C. and most preferably within 5 C. of, but below, that at which the fibers are sufliciently softened to stick to each other at the conditions at which the treatment is carried out, maintaining it at said temperature for a brief time, typically from 0.5 to two seconds, and thereafter cooling the fiber at least to about 100 C. and keeping it free of substantial tension until the crystal structure of the fiber has become substantially stabilized.

It is not known with certainty what internal changes take place in polypropylene fiber during the crimping step according to this invention. However, it is believed most likely that when a polypropylene fiber is heated according to this invention, a substantial portion of the crystalline structure is destroyed while another substantial part still retains its crystalline order. This, then, results in a rapid build-up of internal localized stresses which cause immediate irregular deformaton of the fiber.

The method of this invention comprises a very simple processing step which can be included in the production of polypropylene fiber and fiber products without substantial addition investment of capital and which results in rapid and inexpensive conversion of straight filament, staple or yarn or products thereof into crimped or bulked filament, staple or yarn or products thereof, in which the fibers have a permanent irregular three dimensional crimp. The crimping method of this invention results in fibers having useful physical properties for textile applications. The resulting crimp may be varied withn a wide range of tightness or looseness; yarns crimped according to this invention correspondingly may have varying degrees of bulkiness.

3 THE APPARATUS OF THIS INVENTION While the above described method of this invention can be carried out in a variety of different apparatus, as described hereafter, a particularly advantageous apparatus has been invented to carry out the method and is described and claimed herein. Briefly, it consists of means for feeding a continuous filament or yarn; means for guiding the filament or yarn through a tube; means for surrounding the filament or yarn in said tube with a gaseous atmosphere of controlled temperature, preferably arranged such that a flowing stream of vapor of controlled temperature contacts the yarn or filament immedi ately upon its entrance into the tube and flows co-currently with its direction of travel; means for cooling the filament or yarn after it issues from the tube; and means for guiding it to a takeup device, adapted to keep the filament or yarn under a minimum of tension until it has been cooled sufiiciently to substantially stabilize its crystal structure.

OBJECTS OF THIS INVENTION The objects of this invention include the following:

To provide a simple, generally applicable, non-mechanical method for producing crimped polypropylene fibers and yarns;

To provide polypropylene fibers and yarns having an improved irregular crimp;

To provide a method of crimping polypropylene fibers and yarns in which the degree of crimping can be readily and simply controlled over a wide range of frequency and amplitude;

To provide an apparatus for carrying out the novel crimping method of this invention in a simple, practical manner.

Other objects will appear from the following description of the invention.

The invention is described in part by reference to the drawing, wherein:

FIGURE 1 is a schematic idealized projection of a portion of a crimped fiber;

FIGURES 2A through 2N are representations of polypropylene filaments produced at various difierent crimping conditions, and illustrating different degrees of crimps;

FIGURES 2P, 2Q and 2R show other filaments for comparison purposes;

FIGURE 3 is a schematic drawing of the preferred This invention is particularly adapted to the produc tion of crimped fibers from resins consisting predominantly of stereoregular, and particularly isotactic, polypropylene. Following conventional terminology, reference to crystallizable or stereoregular polypropylene means, unless the context indicates otherwise, solid polypropylene having a high degree of stereoregularity, reflected in at least crysallinity, usually between 60 and 70%, as determined by X-ray diffraction analysis, infrared analysis or comparable methods, when solidified under conditions which favor crystallization. In general this type of polypropylene contains at most only a very small proportion of material which is extractable in paraffinic hydrocarbons of up to gasoline boiling range. Typically, the proportion of highly crysallizable polypropylene which is extractable in boiling heptane or isooctane is less than 10% and usually less than 5%. The viscosity average molecular weight of such stereoregular polypropylene is usually at least about 40,000 and generally between 100,000 and 1,200,000. For convenience the molecular weight is usually indicated by intrinsic viscosity. The intrinsic viscosity of polypropylene, measured in decalin at 150 0., expressed in dl./g., may be as low as 0.5 or less and as high as 10 or more. For melt spinning, crystallizable polypropylenes having intrinsic viscosities between 1.3 and 4.5 are ordinarily employed, and those with intrinsic viscosities between 1.5 and 3 are preferred. Polymers of intrinsic viscosities down to about 0.5 may sometimes be used. As is well known, there may be a decrease of intrinsic viscosity due to degradation during melt spinning.

Polypropylene may be modified prior to extrusion, for example, by deliberate addition of small proportions of atactic polypropylene or of another alpha olefin polymer.

Antioxidants and U.V. stabilizers, of which a great variety are now known, are usually added prior to extrusion. The group of suitable antioxidants comprises 2,6-di-tert.butyl-4-methylphenol, bis(2-tert.butyl-5-methyl- 4-hydroxyphenyl) sulfide, 1,1,3-tris(2-methyl-6-tert.butyl- 4-hydroxyphenyl)butane, 1,3,5-trimethyl-2,4,6-tri(3,5-ditert.butyl-4-hydroxybenzyl)benzene, oxycresyl camphene, zinc dibutyl dithiocarbamate, and many others, and combinations of such compounds with sulfur compounds such as dilauryl thiodipropionate or dicetyl sulfide.

The group of suitable U.V. stabilizers comprises benzophenones such as 2-hydroxy-5-dodecoxybenzophenone, 2-hydroxy-5-octoxybenzophenone; complexes such as the nickel phenolate of a monosulfide of bis(p-octylphenol); benztriazine derivatives, and many others.

Polypropylene may be further stabilized by addition of other additives of the type heretofore used in stabilizing polyvinylehloride, as elaborated in US. 2,985,617 to Salyer et al.

Polypropylene may be modified by incorporating therein organic molecules or organic or inorganic compounds of metals to provide dyeability characteristics or other improved properties. Polypropylene may also contain substantial proportions of pigments for coloration.

Generally the polymer which is extruded to form fibers according to this invention consists of (a) at least 75% by weight polypropylene which has a crystallizability as determined by known infrared density, or X-ray diffraction techniques, of at least about 50%, and (b) no more than 25% of other materials including suitable additives which provide desired properties, such as stability against degradation caused by heat and ultraviolet radiation. Filament fibers or yarns formed from such compositions are referred to herein for simplicity, as polypropylene filaments, fibers or yarns.

FILAMENTS AND TEXTILES SUITABLE FOR CRIMPING ACCORDING TO THIS INVENTION The crimping process of this invention is applied to polypropylene fibers after they have been extruded and drawn in any manner which results in filaments drawn to at least two times their original length, but at least to the natural draw ratio or its equivalent, i.e., to a condition at which further stretching does not result in necking down of the fibers.

Polypropylene filaments for treatment according to this invention are most suitably produced by melt spinning. This is a well-known process in which polymer is melted in an extruder, extruded through a die having suitable openings, and cooled.

Stretching of melt-spun filaments is a part of known processes. The method of stretching is not critical to success in obtaining a desired crimp according to this invention. Any desired rate or method may be employed including stretching in several stages and/ or at ditferent temperatures.

Stretching is preferably carried out at temperatures between and C. Temperatures below 105 C. are less preferred. Least preferred are temperatures below 80 C.

The crimping process of this invention may be applied to monofilarnents or to multifilaments. The former are typically relatively coarse, e.g., from 30 denier up but may also be as fine as 15 denier or less; the latter are typically relatively fine, e.g., from 30 denier down, and usually between 1.5 and 15 denier. In the case of coarse filaments, crimps are not as tight as those produced when finer filaments or yarns are exposed to similar crimping conditions.

The crimping step of this invention may be carried out on individual fibers, on substantially untwisted yarns, on staple, or on manufactured textiles, particularly hooked or tufted textiles, such as carpeting, produced from stretched polypropylene filaments, untwisted yarns, or staple. The process may also be applied to yarns or textiles consisting of mixtures of polypropylene and other textile filaments which are resistant to brief exposure to the temperature used in the process of this invention.

When the crimping step of this invention is to be applied to yarns or fabrics which have been given a previous textile finishing treatment, it is preferred to first wash off most or all of the finishing material before crimping according to this invention. A water or alcohol wash is usually sufiicient for typical finishes such as low molecular weight polyethylene oxides and their derivatives.

The crimping method of this invention is not effective on tightly twisted yarns. It is important that the individual filaments of a yarn be free to move relative to each other during the heat crimping step. While it is preferred to employ untwisted yarns, it is possible to crimp yarns which have a slight twist. When a twisted yarn is to be crimped, it is first treated to substantially untwist it, as by an air blast.

CHANGES IN PHYSICAL PROPERTIES DUE TO CRIMPING ACCORDING TO THIS INVENTION The crimping step of this invention results in some loss in tensile strength of treated fibers, apparently due to partial deorientation. The tensile strength of the finished products are typically about three-fourths to one-fourth of that of the stretched filaments prior to crimping, and about two to six times that of the undrawn filaments.

Fibers crimped according to this invention will extend uniformly under tensile stress, i.e., without necking.

Elongation at break of fibers crimped according to this invention typically is from about four to about six times that of the stretched fibers prior to crimping.

Typical values, for 15 denier yarns, are presented in the following Table 1.

1 Crimping according to the method of this invention.

CRIMPING The appearance of filaments produced by the process of this invention can be varied at will over a considerable range, particularly by varying the conditions employed in the crimping step. Other factors, e.g., polymer properties and dimensions of the fibers will also affect the appearance of the crimped filaments. Fibers can be produced which have the type of crimping that is characteristic of wool filaments in frequency, amplitude and angularity of the loops and angles in each filament.

FIGURE 2 of the drawing shows drawings of fibers, copied from photographs, at five times enlargement.

FIGURE 2P shows an uncrimped fiber.

FIGURE 2Q shows a filament from a polypropylene yarn which has been crimped in a stuffer box.

FIGURE 2R shows a filament from a Wool yarn, which has a natural crimp.

Crimps produced by the method of this invention are illustrated in FIGURES 2A through 2N.

FIGURES 2A through 2L illustrate the improvement in crimping, carried out in air, as the temperature approaches the sticking temperature of the filaments. The conditions under which crimps 2A through 2L are produced are described in Example 6.

FIGURE 2M illustrates a filament from a yarn crimped in an oil bath, as in Example 4, and FIGURE 2N a single filament dipped in an oil bath at similar conditions.

Attempts to define crimping of filaments or bulkiness of yarns or fabrics in numerical terms depend largely on subjective evaluations or on conditions which may not be completely reproducible. The ultimate criterion is the appearance and feel which the crimped filament contributes to a finished fabric.

For purposes of description of this invention, a crimp rating scale has been devised. It is set out in Table 2. The scale can be correlated with measurements made on enlarged photographs of actual fibers. It is not possible, however, to devise a completely objective scale which takes into account all factors which contribute to the effectiveness of a crimp. Hence, the crimp rating scale of Table 2 is to some extent subjective or 'arbitrary.

In Table 2, the ratings are illustrated by a group of measurements taken on photographs of crimped fibers such as those shown reproduced in FIGURES 2A through 2L of the drawing. The fibers were photographed in a loosely stretched condition, under just sufficient tension to place them in an essentially straight line without significantly distorting the angular crimps.

FIGURE 1 of the drawing, showing an idealized short section of fiber, illustrates crimp angle, amplitude and frequency, as referred to in Table 2.

The number of crimps per unit length (frequency) is arbitrarily defined by counting each angular turn of the fiber as a crimp. In FIGURE 1, angles 1, 2, 3, 4 and 5 each represent one crimp; the illustrated segment thus has 5 crimps. The unit length selected for measurement conveniently is a segment containing 5 crimps.

The angularity of the crimp, measured in degrees of angle, is arbitrarily defined as the average of the angles formed by turns in the direction of the fiber when the fiber is in loosely stretched condition, i.e., just sulficiently stretched to be predominantly in a straight line; where the turn of the crimp is rounded, the angle is determined as illustrated for angle 2 in FIGURE 1. In FIGURE 1 the crimp angularity is the average of angles 1, 2, 3, 4 and 5. It will be evident that the most sharply angled crimp has the smallest numerical value of angularity in degrees of angle.

The amplitude of crimp is the absolute average of the altitudes of the maxima and minima formed in the fiber, drawn to the mean line of the fiber. Positive values are assigned regardless of the direction of deviation from the mean line. In FIGURE 1, the crimp amplitude is the average of a, b, and c. The amplitude may be expressed in units of length or in multiples of the fiber thickness.

It will be evident that there can be a great deal of variability. For example, there may be few crimps per inch, but with strong angularity and large amplitude; there may be very many crimps of very low amplitude and low angularity (i.e., average angles close to and there may be many intermediate conditions. There are additional factors which contribute desirable bulkiness characteristics but which are not measurable in the above numerical terms. For example, the above numerical properties are measured on a two-dimensional projection of the fiber. Crimps produced according to this invention are three-dimensional. Thus, .a crimp in the direction at right angles to the plane of the projection surface will not appear in the projected line, and crimps at other angles will appear reduced in amplitude and angularity. Another type of crimping which is not amenable to the above measurement are the tight loops illustrated in FIG- URE 2N.

TABLE 2.ORIMP RATING SCALE VARIABLES IN THE CRIMPING STEP The degree of crimping obtained according to this invention is primarily affected by the treating temperature, i.e., the temperature at which the crimping treatment is carried out and by the rate of heating to said temperature, and secondarily by the residence time, i.e., the length of time during which the filament is exposed to said temperature.

As the treating temperature closely approaches the sticking temperature, small increases in temperature cause great increases in the degree of crimping at otherwise equal conditions. The optimum residence time is shorter at the higher temperatures. A very moderate degree of crimping may be obtained as much as 15 C. to 10 C. below sticking temperature, especially when the residence time is relatively long, e.g., seconds. The generally desired tight degree of crimping requires a treating temperature within about 5 C., and usually within 1 to 2 C. of the sticking temperature, preferably at residence times of 0.5 to 3 seconds.

The sticking temperature is defined as the temperature at which the fibers stick to each other at the conditions of the treatment. The sticking temperature for isotactic polypropylene fibers is generally in the range from 140 to 160 C., depending somewhat on the precise formulation and previous history of the fibers and on the method of heating and transporting the fibers. The determination of the sticking temperature for a given system is made observing the tendency of the treated fibers to actually stick together as the temperature approaches or exceeds 145 C. at the treating conditions employed in the process.

Heating the fibers up to the treating temperature is preferably carried out as rapidly as possible, for best results, as illustrated hereafter. Slow heating, e.g., over a period of ten seconds or more, results in shrinkage of the fiber without significant crimping.

It has been observed when fibers were immersed in fluid maintained at the desired elevated temperature, that the fibers remain straight during an induction period ranging from a fraction of a second to as long as 1 or 2 seconds, and then suddenly curl up and acquire the ultimate degree of crimp. No additional advantage is gained by maintaining fibers at the crimping temperature after the initial crimping has taken place. Prolonging the heating step beyond a few seconds generally results in undesirable shrinkage with no corresponding improvement in crimp or other beneficial properties. Some decrease in degree of crimping is generally observed on continued residence at the crimping temperature.

An important factor for eifcctive crimping is the substantial absence of tensile load on the fiber while it is being heated. It is most preferred to apply heating while the tensile load on the fiber is no more than that which results from the weight of the fiber and the forces applied by a stream of air or vapor blown against the fiber in the manner which will be described in more detail hereafter. Mechanical load during treatment, if necessary, should be kept as low as possible and should not exceed about 0.001

gram per denier. It has been found that no crimping whatever results when a fiber is kept under substantial tensile load while it is heated under the conditions of this invention.

Upon completion of the heating step the treated fiber is cooled to a temperature of 100 C. or below. This cooling may be conveniently carried out by placing the fiber in air at ambient temperature. There is ordinarily no advantage in shock cooling of the fiber; in fact it may be preferred to subject the fiber to an annealing step at a temperature in the range from to 125 C. and most suitably at about C. The annealing may consist of maintaining the fiber at that temperature for a prolonged period, e.g., from 1 to 24 hours. Annealing results in improvement of the crystalline structure of the fiber with a resultant improved in properties associated with crystallinity such as increases in modulus and tensile strength and decrease in percentage elongation at break.

Cooling of the fiber at least down to 100 C. should take place while the fiber is under no substantial tensile load and the fiber should be maintained in this condition at least until the crystalline structure has stabilized to a substantial extent. This ordinarily occurs within 5 seconds at temperatures below 100 C.

MODES OF PRACTICING THE INVENTION Several modes of practicing this invention will be described below and others will occur to persons of skill in this art.

The steps of extrusion and stretching of filaments which precede the crimping step of this invention may be carried out according to methods well known to the art, as disclosed above. Extruded, stretched filaments may be directly charged to the crimping step or may be stored prior to crimping, e.g., Wound up into kops. It is preferred to subject yarns taken from kops to a loosening treatment, e.g., by a mild blast of air, before they are heated to the crimping temperature.

Batch treatment methods particularly suited to practice of the process on a small scale, described in Examples 3B and 4, involve dipping filament into an air bath or oil bath of controlled temperature. These dipping methods can be adapted to a larger scale by adjusting the size of the air bath or oil bath and quickly inserting masses of loosely arranged filaments into such baths.

A preferred method of practicing the crimping step of this invention is by means of the novel apparatus of this invention. Preferred modes of the apparatus are illustrated in FIGURES 3 and 4 of the drawing and the method is further illustrated by means of Example 6.

The apparatus, as illustrated in FIGURE 3, consists of a yarn-feeding set of Godet rolls 4, guide means 6 and 7 which may be rolls or pins or the like, a straight insulated or heated tube 2, yarn guide means 8, a set of Godet rolls 5 and yarn takeup means 9. The head of tube 2 is illustrated in further detail in FIGURE 4. The head is provided with a narrow opening 11 adapted to admit a single filament or yarn 1 into the tube and with a gas inlet 3 which communicates via line 3a with a blower or other gas driving means, now shown, and a heating means for said gas, not shown. Gas from inlet 3 is passed into tube 2 by multiple, downwardly-inclined noz zles or passages 12 concentrically spaced around the circumference of the tube. These nozzles are suitably simple straight holes, as illustrated. It is important that they be symmetrically spaced around the circumference of the tube to avoid twisting filament or yarn 1 or forcing it against the wall of the tube. It is preferred to arrange nozzles 12 to give a substantial downward direction to the gas. They may be arranged, 1 for example, to form an angle of from 15 to 60 degrees with the axis of tube 2. The drawing illustrates a preferred angle of 30 degrees.

In operating the process of this invention by means of the apparatus illustrated in FIGURES 3 and 4, a polypropylene filament or yarn 1 is supplied from supply means not shown, passed over Godet rolls 4 and guides 6 and 7 and then into tube 2 by means of the relatively narrow passage 11. Hot air, steam or other gas at a controlled predetermined temperature is passed from line 3 via nozzles 12 into tube 2. The term gas as used herein, comprises any inert gas or vapor, i.e., a gas or vapor that does not exert any undesirable chemical action on the filament. Air is satisfactory, and is generally preferred.

Other gases which are non-reactive with polypropylene at the conditions of the process include, for example, nitrogen, noble gases, natural gas, or live or superheated steam.

As illustrated, the dead space between the nozzle opening and the top of the tube is kept as small as conveniently possible to provide the most rapid practical heating of filament 1. The filament and gas pass downwardly through tube 2, the gas stream simultanously heating and providing the moving means for the filament. The bottom of tube 2 is suitably completely open to provide unimpeded egress for gas and yarn or filament.

The temperature of the gas is controlled to maintain the condition in the tube such that the yarn or filament is slightly below its sticking point. The sticking temperature may be determined by a test in separate apparatus, but is best determined at the beginning of a run by slowly increasing the gas temperature until sticking is just observed in the treated yarn or filament, and then dropping the temperature at least about 1 C., but not below that at which the desired degree of crimp is obtained. Sometimes it may be desirable to raise the feed rate or adjust the gas rate at this point, since this may permit crimping at a somewhat higher temperature without sticking.

The yarn or filament leaving tube 2 is suitably cooled in air at room temperature, i.e., between about 20 and about 30 C. Yarn may be permitted to drop to the floor below the tube and picked up from there and guided through Godet rolls to takeup device 9. If desired, the yarn may be permitted instead to form a short catenary arc between the bottom of the open heating tube and the Godet roll, as illustrated. Care must be taken that no substantial tension is applied to the yarn in the heating tube itself and up to the time at which it has cooled at least to a temperature no higher than 100 C. and its crystal structure has had time to stabilize. Godet rolls 5 can be adjusted such that no substantial tension is applied to the yarn up to that point; takeup means 9 may be removed sufliciently far from Godet rolls 5 so that the total travel time of the yarn from its exit from tube 2 to its being taken up on takeup roll 9 is sufficient to provide the desired crystal stabilization.

While the above illustrates the preferred apparatus and method of practicing this invention it will be understood that various modifications can be made without departing from the spirit of the invention. It will also be understood that various auxiliary equipment such as supporting means for the tube, heat sensing devices, insulating or heating means for tube 2, and the like have not been illustrated.

It should be understood that tube 2 need not necessarily be vertical. The movement of the yarn through the tube is effected essentially by a co-currently flowing vapor steam and the method may therefore be conducted in tubes in other than vertical position. However, the tube must be an essentially straight tube in order to provide unimpeded travel for the filament or yarn.

Contrary to What might be expected, better crimping is obtained when conditions in the apparatus are adjusted such that the yarn is not twisted in the tube.

It will be evident that the residence time of the filament at the desired temperature is a function of the rate of travel of the filament through tube 2 (taking into account filament shrinkage), the length of the tube 2 and the temperature maintained in tube 2. In the preferred method of operating the process, conditions are adjusted such that a substantially uniform temperature preferably within 2 C. but just below the sticking temperature of the yarn or filament, is maintained throughout the length of tube 2 and the rate of travel and length of the tube are selected such that the residence time in the tube is only slightly greater than the crimping induction period. For example, if the obesrved induction period is second the residence time in the tube is preferably adjusted to be no more than about 1 seconds. It will be realized that the tube may be designed to consist of multiple segments so that its length can be readily adjusted between runs. Other variations of the process and apparatus of this invention will occur to the person skilled in the art.

One commercial method for production of polypropylene staple is easily modified to take advantage of the present invention. In this method polypropylene yarn is carried on a belt to a chopper and the resulting staple is then conveyed by an air stream to a gathering device. According to this invention, uncrimped yarn is fed to the chopper. The air stream in which the staple is picked up is maintained at the desired elevated temperature required for crimping for the desired period of time and thereafter cooled by any suitable method, e.-g., addition of cool air.

In some commercial methods of producing polypropylene filaments there is a processing stage in which the filaments are carried under no load on a moving belt. This may be in a drier or in ambient air. The crimping process of this invention can be applied by passing such a belt through a heated zone of sufiicient length to provide the desired contact time and the desired elevated temperature. This may be achieved, for example, by passing the belt through a zone in which the filaments are quiclcly heated to the desired temperature by means of heated air or other inert vapors, by heating lamps, or by other means.

The invention will be better understood from the following examples. The examples are illustrative of the invention and of preferred modes of practicing it, but the invention is not limited by the examples.

The yarns and filaments employed in the examples are produced by melt extrusion of stereoregular polypropylenes having the following properties:

Sample A Sample B Intrinsic Viscosity 1 1. 9 2. 5 Crystallinity 2 65-70 65-70 1 Measured in deealin at 150 C. 2 By density measurements.

The polypropylenes contain conventional stabilizing additives.

Yarns and filaments illustrated in the example are produced under the following conditions on industrial size equipment:

Sample A Sample 13 Takeup speed, ft./min 3004500 300-600 Stretch ratio 3:1 7:1 Drawing temperature C. O. Yarn l 1,800/90/20 1 860//6 'lotal denier/number of filaments (ends)/nominal denier of single filament.

Example 1 TABLE 3 Yarn Sample Unstretched Stretched, Stretched Stretched, Stretched uncrimped and uncrimpcd and crirnped crimped Denier 3O 20 -25 6 8. 2 Tensile strength at break g. den 8 2.8 2.0 6. 4. Elongation at break, percent 850 37 225 23. 6 75 Example 2 and kept there :for a brief time, of the order of one min- Yarn A was annealed, after crimping, by keeping it under no tensile load in air at 100 C. for 24 hours. Table 4 shows the results of this annealing step. The general effect of annealing is to increase crystalline order and thus to change those properties associated with crysta'll-inity. Annealing does not noticeably affect the degree of crimp of the fibers.

Part A.-It was found that slow heating of a stretched yarn such as yarn B of Example 1, results in shrinking of the yarn without noticeable crimping. For example, a laboratory oven was brought to a temperature of about 2 C. below the observed sticking temperature of the yarn. The laboratory oven was then opened and a sample of yarn on a tray was placed in the oven. Opening the oven for the time required to place the tray in it resulted in a drop in temperature in the oven. The oven was closed; it took at least 1 minute for the temperature rise back to the previous level. The yarn was kept in the oven a brief additional time after it had reached the predetermined temperature. Upon removal of the yarn from the tray it was found to have a slight waviness of low amplitude and of about one inch wave length. This waviness would be rated little better than zero on the crimping rating scale of Table 2.

Part B.In a comparison experiment, to illustrate the effect of rapid heating, a wide test tube was placed in an oil bath until the air in the lower part of the test tube had reached the equilibrium temperature (147 C.) which was within about 2 C. of a predetermined fiber sticking temperature. A short length of untwisted yarn B was then rapidly plunged into the lower part of the test tube ute. On removal from the test tube and cooling in air the yarn was found to have a moderate crimp, which would rate about 2 on the crimp rating scale of Table 2.

Example 4 An oil bath was brought to a temperature (147 C.) within about 2 C. of a predetermined fiber sticking temperature A short length of untwisted yarn B was rapidly plunged into the oil bath, kept there for a few seconds and then removed, washed with acetone and dried in a stream of cool air. The resulting yarn had an excellent, tight crimp which would rate 4 on the crimp rating scale. A single filament of the yarn is illustrated in FIGURE 2M.

Example 5 A small portion of rug was prepared by a conventional hooking process, employing uncrimped yarn B and making extra long loops to allow for some subsequent shrinkage. The sample of rug was dipped to half its length into an oil bath similar to that of Example 4, retained therein for a few seconds, removed, washed with acetone and dried in an air stream as in Example 4. It was found that a tight crimp was produced in the yarn loops. The texturized sect-ion of the sample had a bulky pile and was suitable for a carpet, in contrast to the untreated portion which had essentially no bulk and would not be satisfactory as a carpet.

Example 6 A series of runs were made at varying conditions in the continuous apparatus illustrated in FIGURES 3 and 4. Previously stretched yarn produced from Sample B of Example 1 was fed from a kop over a set of Godet rolls, through a narrow opening into the top opening of a 7-foot long, l-inc-h diameter, vertical heated tube. Air was introduced at a controlled temperature and controlled rate at the top of the tube, flowed down through the tube and carried the yarn with it. Temperatures were measured at intervals along the tube. Yarn was guided from the bottom of the open tube to a conventional windup device.

Residence times in the tube ranged from over one second to under 3.4 seconds.

The conditions and results of a series of runs are illustrated in Table 5.

TABLE 5 Temperature readings, C.

Feed Crimp Illus- Examples 1 it. 3 ft. Bottom rate, rating trated in Inlet below below of ftjmin. figure air top of top of tube tube tube 143. 0 146. 3 147. 0 146. 7 250 1 2A. 144. 9 147. 6 148. 9 149. 4 250 1 2B. 147. 0 150. 0 151. 8 152. 3 250 2 2C. 147. 0 150.0 151. 8 152. 3 400 1 2D 149. 3 152.0 152. 9 152. 4 350 4 2E. 149. 3 152. 0 152. 9 152.4 250 4 2F. 149. 3 152.0 152. 9 152.4 390 4 2G. 151. 7 154. 5 156. U 155. 5 250 3 2H. 151. 7 154. 5 156. 0 155. 5 340 3 21. 153. 8 155. 5 158. 0 157. 5 250 3 2]. 154.8 156. 8 158. 0 1 340 3 2K. 155. 5 157. 5 159. 5 158 250 4 2L.

Projection of segments of fibers produced in the above examples, copied from photographs taken with about five times enlargement, are shown in FIGURES 2A through 2L of the drawing, as identified above.

The sticking point for this yarn was found to occur when the temperature in the tube was raised about 1 C. above the temperatures shown in Example 6-12, i.e., to a maximum temperature of about 160.5 C, measured 3 feet below the top of the tube.

Relatively poor crimps were obtained in Examples 61 to 6-4, whose maximum temperatures were 13.5 to 8.7 C. below the sticking temperature. Good to excellent crimps were obtained in Runs 6-5 through 6-12, with maximum temperatures from 7. 6 to 1 C. below the sticking temperature.

I claim as my invention:

1. The method of crimping previously stretched fibers of predominantly crystallizable polypropylene which comprises rapidly heating the fibers while free of substantial tension to a treating temperature which is within 15 C. of, but below, the temperature at which two fibers of the same composition would adhere to each other, maintaining the fibers at said treating temperature for a time not exceeding 10 seconds, and sufiicient to result in formation of a crimp in said fibers, and thereafter cooling said fibers at least to about 100 C., and keeping them free of substantial tension until the crystal structure of the fibers has substantially stabilized.

2. The method according to claim 1 where-in said previously stretched fibers are fibers that have been stretched at temperatures between 105 and 145 C. to at least two times their original length and at least to the natural draw ratio.

3. The method of crimping previously stretched fibers of crystalline polypropylene, said fibers having been produced by melt extruding polypropylene and stretching the resulting filaments between and C. to at least two times their original length and at least to the natural draw ratio, which method comprises rapidly heating said fibers while free of substantial tension to a treating temperature which is within about 10 C. of, but below, the temperature at which two fibers of the same composition would adhere to each other, maintaining the fibers at said treating temperature for a length of time in the range from about /2 to 10 seconds, suflicient to result in formation of a crimp in said fibers, and thereafter cooling said fibers at least to about 100 C., and keeping them free of substantial tension until the crystal structure of the fibers has substantially stabilized.

4. The method according to claim 3 in which said fibers are treated as an untwisted yarn and said heating is carried out within 5 C. of said adhesion temperature by suddenly contacting said yarn with heated fluid in vapor phase.

References Cited by the Examiner UNITED STATES PATENTS 2,993,333 6/1961 Bergh et al 28-62 X 3,019,507 2/1962 Maragliano et a1. 28-72 3,048,467 8/1962 Roberts et a1. 28-1 3,137,989 6/1964 Fior et a1 2872 3,241,212 3/1966 Evans et al 28-1 MERVIN STEIN, Primary Examiner.

DONALD W. PARKER, Examiner.

L. K. RIMRODT, Assistant Examiner. 

1. THE METHOD OF CRIMPING PREVOUSLY STRETCHED FIBERS OF PREDOMINANTLY CRYSTALLIZABLE POLYPROPYLENE WHICH COMPRSIES RAPIDLY HEATING THE FIBERS WHILE FREE OF SUBSTANTIAL TENSION TO A TREATING TEMPERATURE WHICH IS WITHIN 15*C. OF, BUT BELOW, THE TEMPERATURE AT WHICH TWO FIBERS OF THE SAME COMPOSITION WOULD ADHERE TO EACH OTHER, MAINTAINING THE FIBERS AT SAID TREATING TEMPERATURE FOR A TIME NOT EXCEEDING 10 SECONDS, AND SUFFICIENT TO RESULT IN FORMATION OF A CRIMP IN SAID FIBERS, AND THEREAFTER COOLING SAID FIBERS AT LEAST TO ABOUT 100*C., AND KEEPING THEM FREE OF SUBSTANTIAL TENSION UNTIL THE CRYSTAL STRUCTUAL OF THE FIBERS HAS SUBSTANTIALLY STABILIZED. 